The invention relates to method and apparatus for stressing laminated pieces to achieve a straight line resultant piece with thin laminar stock by balancing the laminating stress against the inherent stress in the fold of the material. Particularly, the method and apparatus of the invention is related to folded trays and one piece folding boxes made from pre-cut box blanks. A preliminary examination of prior art has developed the following U.S. Pat. Nos.: 1,899,652, Stortz, Feb. 28, 1933; 1,959,235, Goss, May 15, 1945; 1,962,638, Czerweny, June 12, 1934; 1,979,993, Peck, Nov. 6, 1934; 2,469,641, Goss, May 10, 1949; 2,808,766, Larsen, Oct. 8, 1957; 2,863,370, Dorfman, Dec. 9, 1958, 2,957,395, Meyer, Oct. 25, 1960; 3,101,653, Burden, Aug. 27, 1963; 3,459,105, Waldbauer, Aug. 5, 1969; 3,521,536, Waldbauer, et al, July 21, 1970; 3,584,548, Brown, June 15, 1971; 3,913,465, Keck, Oct. 21, 1975.
The process of the invention affords a method whereby box blanks of many materials may be formed into a shell or tray and further provides steps whereby the tray may be folded into a closed one-piece box. The method provides an interval during closing wherein goods may be loaded into the box. The process is distinctive with respect to prior art in applying pressure to both sides of doubled or tucked end flaps to achieve a stressed condition during adhesion which balances the stress in the box blank material adjoining the score lines of the end flaps such that the tucked end flaps approach a straight line and right angle configuration at the fold line to form a neater box appearance and to aid closure. In addition the process provides a step wherein the formed tray stage is grasped at the hinge panel to be drawn through the box closing stages and affords dwell time for loading the box before closure.
The preferred apparatus for implementing the process is in part distinct from said prior art in being comprised of a forming assembly with forming plates having converging concave and convex pressure segments for stressing the tucked end flaps of the box blank during the adhering stage of the end flaps, and in further comprising vacuum means adapted to grasp the tray hinge panel for tray separation from the forming assembly and moving the formed tray format of the blank through box closing elements.